The present invention relates to the printing and/or copying arts. It finds particular application in conjunction with the production of photoreceptor belts for electrophotographic copiers, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications where it is desired to apply a plurality of coatings with even thicknesses to a web material.
In the case of electrophotographic devices such as, e.g., copiers, it is known to employ a photoreceptive belt to form latent electrostatic images within the device. Belt type photoreceptors typically include a photoreceptive material applied to a polymer or other like continuous web which is moved about an arrangement of rollers. Belt type photoreceptors generally have larger photoreceptive surfaces as compared to drum type photoreceptors, and accordingly, can hold more latent images per cycle. Hence, belt type photoreceptors are often employed in higher-end electrophotographic devices or like applications where high speed is desired.
The photoreceptive material applied to the web may include as many as four separate layers. The four layers include: a first layer (nearest to the web) known as the undercoat layer; a second layer known as the charge generation or binder generator layer, i.e., where the charge is actually generated by converting photons into electrostatic charge; a third layer known as the small molecule transport layer; and a optional fourth or top layer (farthest from the web) known as the overcoat layer. Coating techniques suitable for applying the layers are known in the art. However, many of the previously developed techniques suffer insomuch as they only apply a single layer at a time. This is disadvantageous to the extent that the manufacturing of the photoreceptive belt then involves as many coating operations as there are layers. When coating one layer at a time, photoreceptor belt production can be undesirably time consuming.
Generally, uneven thickness in the layers of the photoreceptive material results in performance degradation of the belt. Accordingly, it is desired that each layer have a substantially uniform thickness across the web. For example, manufacturing specifications for the small molecule transport layer, which is typically the thickest layer, may have a tolerance of plus or minus one-half of a micron over a web that is a thousand feet long by forty inches wide. Unassisted coating techniques suffer to the extent that they cannot provide the uniformity of thickness desired. Many unassisted techniques have a limited coating thickness uniformity, e.g., in the neighborhood of plus or minus two percent. Consequently, ultrasonic assisted coating techniques have been developed which aid in achieving a uniform thickness for a coating layer. However, to date, the developed ultrasonic assisted coating techniques have been limited to applying a single layer at a time with the ultrasonic energy being introduced through the entire die or from behind the web. For multi-layer applications, such an introduction of the ultrasonic energy can have undesired effects. For example, the locationally generalized application of ultrasonic energy through the entire die may cause the layers to become undesirably intermixed, or insomuch as the ultrasonic energy is introduce from the back side of the web and has to travel through the layers, the effects may be significantly different in the various layers due to the relatively different acoustic impedances thereof.
The present invention contemplates a new and improved multi-layer slot coating die with ultrasonic assist and/or associated method which overcomes the above-referenced problems and others.
In accordance with an aspect of the present invention, a multi-layer slot coating die is provided. The die includes a housing having a cavity therein, and a divider arranged within the cavity of the housing such that a plurality of separate channels are defined therein. The channels have elongated openings on an output side of the die from which layers of coating material are extruded, and an ultrasonic transducer is mechanically coupled to the divider.
In accordance with another aspect of the present invention, a method is provided for coating a web with a plurality of layers of coating material. The method includes: advancing the web in a first direction; in a second direction transverse to the first direction, extruding the plurality of layers of coating material onto the advancing web such that there is a contact interface between two of the layers; and, applying ultrasonic energy to the contact interface.
In accordance with yet another aspect of the present invention, a multi-layer slot coating die includes a housing having a cavity therein. The housing includes first and second portions. The first portion contacts an upstream meniscus which is formed as layers of coating material are extruded from an output side of the die onto an advancing web, and the second portion contacts a downstream meniscus which is formed as layers of coating material are extruded from the output side of the die onto the advancing web. The die also includes a divider arranged within the cavity of the housing such that a plurality of separate channels are defined therein. The channels have, on the output side of the die, elongated openings from which layers of coating material are extruded, and an ultrasonic transducer mechanically coupled to at least one of the divider, the first portion of the housing and/or the second portion of the housing.
One advantage of the present invention is that it provides for multi-layer coating.
Another advantage of the present invention is that it provides for even layer thickness via ultrasonic assistance.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.